T lymphocytes require macrophage help in order to proliferate in vivo in response to mitogens and antigens. The compound phorbol myristate acetate (PMA) will replace macrophages and enable T cells to proliferate in response to a mitogenic but not an antigenic stimulus. T cells primed with PMA will also proliferate in response to a soluble product derived from the culture of antigen pulsed macrophages. We are currently examining the product in the culture supernatant of antigen pulsed macrophages to see if it exhibits the theoretically predicted properties of "processed antigen"--i.e., antigen specificity and genetic restriction in its effect or if it is a non specific T-cell triggering molecule.